1. Field of the Invention
The present invention relates to an input apparatus, a control method for the input apparatus, and a program causing a computer to execute the control method for the input apparatus.
2. Description of the Related Art
There is an input apparatus which detects a proximity state of an operation body such as a finger by measuring a physical quantity such as electrostatic capacitance at a plurality of detection positions in a detection region. An input apparatus as an example includes a plurality of driving electrodes which are disposed in a certain layer and are parallel to each other, and a plurality of detection electrodes which are disposed in another layer and are parallel to each other, and an intersection position between a driving electrode and a detection electrode is a detection position.
As a driving method for acquiring an electrostatic capacitance at a detection position, there is encoding driving. In encoding driving, for example, a plurality of operations are repeatedly performed in which driving signals with one of positive and negative polarities are simultaneously applied to a plurality of driving electrodes, and detection signals are also measured by the detection electrodes. An electrostatic capacitance at a detection position is calculated on the basis of the obtained detection signal and the driving signal.
International Publication No. WO2009/107415 is an example of the related art.
Generally, a plurality of driving electrodes are arranged at equal intervals, and detection electrodes are also arranged at equal intervals. Thus, if a detection region is rectangular, any number of detection electrodes is associated with the same number of detection positions. On the other hand, a detection region may be desired to have various shapes other than a rectangular shape. If the detection region has a shape other than a rectangular shape, the number of associated detection positions may differ between detection electrodes. In this case, in encoding driving of an input apparatus of the related art, the same driving signal pattern is used for all detection electrodes regardless of the number of detection positions.
If the same driving signal pattern as that of detection electrodes with a large number of detection positions is used for detection electrodes with a small number of detection positions, the balance between positive and negative polarities of a detection signal collapses, and thus levels of detection signals of the detection electrodes with a small number of detection positions increase. In other words, if the number of positive detection signals is larger than the number of negative detection signals, a signal obtained by combining the signals tends to have a signal level which is higher in the positive polarity. If the number of negative detection signals is larger than the number of positive detection signals, a signal obtained by combining the signals tends to have a signal level which is higher in the negative polarity. If a dynamic range is adjusted with respect to a detection electrode having a higher signal level, there is a disadvantage in that the sensitivity of a detection electrode with a lower signal level is reduced. If the level of the detection signal increases, there is also a disadvantage in that noise increases.